My friend is from Arts,HSC Maharashtra board, which topics of English grammar she should prefer to have 80+ score in English Subject ?

Yes you can.sir

Hello,Firstly, I will mention the syllabus of whole grammer portion of the exam and then will work on them. Grammer has 15% weightage in exam.Syllabus: The Tenses – Advanced level of the tenses learned up to secondary level  Types of sentences (Simple, Compound, Complex, Relative clauses)Clauses (Proper usage and synthesis)Verbs of perception (Uses of see, hear, smell, feel, taste and know, have, own think, etc)Voice (Statements, questions, indirect objects, object + object complement, negatives. (Advanced level) (Conversion))Reported Speech (Advanced level, continuous short paragraph consisting of three to four connected sentences)Collocation (The co-occurrence of lexical items)Uses of ‘too’ and ‘enough’ (Conversion and synthesis)Modal Auxiliaries (Will, shall, can, could)Articles (Uses and omission of ‘a’, ‘an’, ‘the’)Prepositions (Indicating time, place and direction)Linking words/discourse markers (Use of linking words in sentences and in larger units)Word formation (Changing word forms-nouns, verbs, adverbs, adjectives)Infinitives, Gerunds and Participles (Usage and synthesis)Look any of the topic can't be left as all are important. But we can club them and then work. So, this way it will reduce the burden as well as due to interrelation it would be easy in studying and applying it.Tenses+voice+reported speech, modals+articles+prepositions+infinitives+gerunds+participles+linking words+use of too and enough, lexical words(noun,verb, adverb, adjective)+word formation, clauses+types of sentences.I have clubed the topics of same kind together, it will be easy for her to study. Pick the easy one first so that they will get completed. Also, download previous year papers along with model papers for practice. And also ask her not to fully rely on this. she also focus on the other parts of the paper for scoring good marks.I hope this helps you.All the best !!